The major professional activity will be research on the function of sleep. The ubiquity of sleep suggests that it serves a vital biological function. Yet there is controversy over whether sleep deprivation produces significant physiological impairment. Cell loss and death were reported in earlier studies, but they could have resulted from stress and fatigue rather than sleep loss. Our research will use a deprivation procedure with appropriate controls. An experimental and a control rat are simultaneously housed each on one side a of horizontal disk mounted over water. EEG and EMG are continuously recorded and scored automatically. When sleep is detected in the experimental rat, the disk is automatically rotated and the rats must move to avoid the water. The experimental rat is sleep deprived, but the control rat gets almost normal sleep. Twelve yoked pairs of experimental and control rats will be compared on food and water intake, weight, temperature, EEG amplitude, and gross behavior during the procedure. Pilot results indicate that experimental rats approach death after 1 to 3 weeks. At this point, both rats will be sacrificed and compared on the following: gross necropsies and histological features of spleen, kidney, mesenteric node, liver, lungs, thyroid, parathyroid, thymus, adrenals, stomach, duodenum, and bladder; number of mitotic figures in the duodenum; chromatolysis and demyelization in brain and spinal cord structures; white blood cell counts; corticosterone levels; and immune function. The results should establish whether sleep is necessary for physiological health and which organs are most affected by sleep loss. We will continue on-going studies on the visual appearance of dreams, the characteristics of rebound sleep, and the role of the suprachiasmatic nucleus in controlling the circadian sleep rhythm.